Cogeneration system (CGS) is one of the promising options to improve CO2 emission of electric power generation systems in Japan. The study aims at clarifying energy performance and CO2 emission factor of various CGS technologies such as diesel engine, gas engine, gas turbine and fuel cell. In the study we propose a new method to convert net heat supply of CGS including the absorption typed heat pump into equivalent electricity comparing with energy performance of the electric typed heat pump.From the method it is deduced that CO2 emission factor of CGS is stood for by kg-CO2/kWh. The method enables to calculate the CO2 emission factors of various CGS technologies and compare their factors of CGS with those of electric power generation technologies. The study also analyzes marginal costs of CO2 improvement if CGS is installed into the system of the existing electric power generation mix. The marginal costs are calculated for two different CGS installations; the supply option for the increased electricity demand and the substitute option for the existing power plant with the same fuel as CGS. It is clear that GE and PAFC are the promising CGS options whose marginal costs are lower among various CGS technologies.
To understand agglomeration phenomena of ash particles in a hot gas ceramic filter system, actual tests were carried out on candle filters with a 4MWth pressurized internally circulating fluidized bed boiler (PICFB) pilot plant. A coal ash build up on the ceramic filter was used in this study. The ash was treated at 850, 900, 950 and 1025°C in an atmosphere of air for 5 minutes in order to make agglomerated particles at known conditions. These samples analyzed by computer controlled scanning electron microscopy (CCSEM) and thermo-mechanical analyzer (TMA). The samples treated at 850 and 900°C showed little sign of agglomeration, while those at 950 and 1025°C produced some agglomerate powders. The index of R2O/ (Al2O3+SiO2) (R2O=Na2O or K2O) for the samples decreased with increase in treatment temperature, and the particle size of the potassium rich particles in the sample shifted to the larger range of 2.2 to 10m. The shrinkage of ash layer measured by TMA was less than 1% at the exposure temperatures of 750 to 800°C and c.a. 2% at that of 850°C after 40 hour tests. However, it exceeded over 3 to 6% at a temperature above 950°C after 40 hour tests. This result showed that heavy agglomeration of ash particles starts from the potassium rich particle suirounded by ash particles and produce a little amount of liquid in ash layer above 960°C, which was also confirmed by thermodynamic equilibrium calculation.
A laboratory scale pressurized fluidized bed combustion (PFBC) system was designed and constructed to clear the details of combustion of coal in PFBC. This PFBC system allows visual observation of hot fluid-ized bed by using a transparent electric furnace. To simulate the emission characteristics of coal combustion of the full scale PFBCs by this lab-scale PFBC, a new similarity rule was introduced. Volumetric heat input and mean gas residence time through fluidized bed in lab-scale PFBC were adjusted to the values matching those of full scale PFBCs. Motion of bubbles and burning of coal particles and volatiles were recognized by visual observations. Volatiles burned mostly in the bottom region of the fluidized bed. On the other hand, char particles burned uniformly in the bed. Ranges of conversion of fuel-N to NO agreed with those obtained in a full scale PFBC. Thus, it is verified that new similarity rule explained above is useful to simulate the combustion behaviors in full scale PFBC by a laboratory scale small PFBC. Effects of operating pressure and O2 partial pressure in flue gas on NO emission were examined. Linear relationship between O2 partial pressure and NO emission was observed. NO emission was decreased rapidly with increasing in operating pressure at constant O2 partial pressure. This may be caused by an enhance-ment of NO reduction by char particles because of increase in number density of char particle in the bed at elevated pressure. In order to confirm this assumption, initial combustion rate of char in the pressurized fluidized bed condition was measured. Initial combustion rate of char increased with 0.6th power of operating pressure. This means that char number density is increased in elevated pressure condition. One of the major reasons to achieve the low NOx emission in PFBC condition, should be the reduction of NOx by char particles through the bed.